Transfer molding systems employed for integrated circuit packaging generally utilize hardened steel mold surfaces to clamp onto the lead frame or packaging substrate, forming the mold cavity.
Such transfer molding systems, however, are poorly suited where the lead frame or packaging substrate has local thickness variations. Either leakage of the encap-sulating material or damage to the packaging substrate (e.g., damage to the conductive traces thereon) may result. any wire bonds, and the packaging substrate 204 exposed to the cavity 205. However, a portion of the upper mold portion 202 in mold system 200 contacts the active area 206 of the integrated circuit die 203 to prevent injected encapsulating material from contacting that surface 206. The active area 206 is thus left exposed after packaging.
In the present invention, lower mold portion 201 comprises hardened steel 207 covered by a relatively soft, deformable material 208. Therefore non-planarity of the adhesive between the integrated circuit die 203 and the packaging substrate 204, and consequent “tilt” of the integrated circuit die 203 with respect to the packaging substrate 204 and the surface of upper mold portion 202 that contacts the active area 206, is compensated by deformation of the relatively soft material 208 (and possibly minor, localized deformation of packaging substrate 204). No gap between the active area 206 and upper mold surface contacting the active area remains into which injected encapsulating material may flow.